Application States

Ans : 

Before iOS 4.0 there were 3 states. Not running, inactive and active.

1. Non-running - The app is not running.
2. Inactive - The app is running in the foreground, but not receiving events. An iOS app can be placed into an inactive state, for example, when a call or SMS message is received.
3. Active - The app is running in the foreground, and receiving events.
4. Background - The app is running in the background, and executing code.
5. Suspended - The app is in the background, but no code is being executed.

For maintaining above states, there are following app delegate methods:

application:willFinishLaunchingWithOptions (First method)

Method called when the launch process is initiated. This is the first opportunity to execute any code within the app.

application:didFinishLaunchingWithOptions

Method called when the launch process is nearly complete. Since this method is called is before any of the app's windows are displayed, it is the last opportunity to prepare the interface and make any final adjustments.

applicationDidBecomeActive

Once the application has become active, the application delegate will receive a callback notification message via the method applicationDidBecomeActive.

This method is also called each time the app returns to an active state from a previous switch to inactive from a resulting phone call or SMS.

applicationWillResignActive

 Each time a temporary event, such as a phone call, happens this method gets called. It is also important to note that "quitting" an iOS app does not terminate the processes, but rather moves the app to the background.

applicationDidEnterBackground

This method is called when an iOS app is running, but no longer in the foreground. In other words, the user interface is not currently being displayed. According to Apple's UIApplicationDelegate Protocol Reference, the app has approximately five seconds to perform tasks and return. If the method does not return within five seconds, the application is terminated.

applicationWillEnterForeground

This method is called as an app is preparing to move from the background to the foreground. The app, however, is not moved into an active state without the applicationDidBecomeActive method being called. This method gives a developer the opportunity to re-establish the settings of the previous running state before the app becomes active.

applicationWillTerminate

This method notifies your application delegate when a termination event has been triggered. Hitting the home button no longer quits the application. Force quitting the iOS app, or shutting down the device triggers the applicationWillTerminate method. This is the opportunity to save the application configuration, settings, and user preferences.

What is localization?

Ans : 

Localization is simply the process of translating your app into multiple languages. However, before you can localize your app, you first need to internationalize it. Internationalization is the process of making your app able to adapt to different languages, regions, and culture. Simple enough, I guess.

So after opening app, we can detect user's locale and change app's language,time accordingly.

Difference Between Inheritance And Extensions?

Ans : 

When to use extension : 
Are you adding general-purpose functionalities that should be available to every UITextField? If so, make an extension. All UITextField instances can call the new methods.

When to use inheritance : 
Are you adding functionality that should be restricted to special instances of UITextField that you would identify precisely? If so, make a subclass. Only the instances of the subclass can use the new methods.

Another diff :

In extension, there is no any specific name of extension in swift, but while subclassing there is another name of subclass.

In extension, we can not add variables (fields), in subclass it is possible to declare variables.

How To Access AppDelegate Methods In Other Class?

Ans : 

let appDelegate: AppDelegate? = UIApplication.shared.delegate as? AppDelegate
appDelegate?.application(UIApplication.shared, didFinishLaunchingWithOptions: nil)

You can make your custom method any called from viewcontroller like :

let appDelegate = UIApplication.shared.delegate as! AppDelegate appDelegate.anyAppDelegateInstaceMethod()

But above is only possible in iOS 10.0 or newer version.

Difference Between If Let And Guard Let?

Ans : 

Basic Difference :

Guard let 

Early exist process from the scope
Require score existing like return, Throw etc.
Create a new variable those can be access out the scope.

if let 

Can not access out the scope.
no need to return statement. But we can write

Note : Both are used to unwrapped the Optional variable.


Guard let

• A guard statement is used to transfer program control out of a scope if one or more conditions aren’t met. 
• The value of any condition in a guard statement must be of type Bool or a type bridged to Bool. The condition can also be an optional binding declaration.

guard condition else { //Generally return }

func submit() {

guard let name = nameField.text else {

    show("No name to submit")

    return

}

If let

• Also popular as optional binding 
• For accessing optional object we use if let

if let roomCount = optionalValue {

        print("roomCount available")

} else {

       print("roomCount is nil")

}

Q. return is mandatory in guard let statement ?
A. Exit is mandatory in guard let statement. So return or throw is mandatory in guard let. Otherwise it gives compile time error.